UFS 8K block size vs RAID array segment/stripe size question

Hi Gurus

I wonder if you can help, I had a SunFire x4100 server attached to a Sun
StorageTek 6140 array configured as 4*500gb disks in a RAID 5 config. We
chose ZFS as our file system which has a default block size of 128k. The
profile we used in the 6140 was the pre-defined SUN_ZFS which has the
segment/stripe size set at 128k which is obviously a perfect match for
the file system block size. Everything ran fantastic, the performance
was great ....however due to a few "other" reasons, this particular test
environment had to be reverted to UFS. So I left the segment/stripe size
on the array at 128k (I had options of between 16k and 512k) and then
newfs'ed the UFS file systems with the default 8k block size and the
performance is really really poor !!

I assume there is a block size vs RAID array segment size issue here
which I need to correct?

Seeing as the array will not allow me to configure the segment/stripe
size to anything less than 16k, what would be the best setting I could
use to get the best performance with an 8k UFS block size ? I assume the
lower I go the better (i.e the lowest 16k setting), and the highest
setting of 512k will give me the worst performance ?? If anybody could
help me understand this or point me to some resources that would be
great

Any help would be greatly appreciated
Gary

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